<form action="user_choose" method="post" id="carform">
    <select form="carform" name="city">
      <option value="城市">城市</option>
      <option value ="北京">北京</option>
      <option value ="上海">上海</option>
      <option value ="广州">广州</option>
      <option value="深圳">深圳</option>
    </select>
    <select form="carform" name="category">
      <option value ="广告行业">广告行业</option>
      <option value=" 4A广告公司"> 4A广告公司</option>
      <option value ="广告策划">广告策划</option>
      <option value ="行销策划">行销策划</option>
      <option value ="广告文案">广告文案</option>
    </select>
      <select form="carform" name="workexp">
      <option value="本科生">本科生</option>
      <option value="本科生以上">本科生以上</option>    
    </select>
    <p><input type = "submit" value = "submit" /></p>
</form>